The present invention relates to a .alpha.-cyanoacrylate-based adhesive composition having good storage stability.
.alpha.-cyanoacrylates of general formula ##STR2## are rapid-setting adhesives which are ideally suited for the adhesion of a large number of materials like rubber, plastics, metal, leather and wood in various technical areas like machine construction, apparatus construction, electrical engineering, jewelery industry, watchmaker industry, household etc. The parts can be joined in an extremely short time of only a few seconds and the adhesive joints produced in this way have good mechanical strength characteristics. The reactive monomers forming the one-component adhesive are hardened mostly in the absence of a catalyst by anionic polymerization initiated by even small traces of extremely weak basic-acting compounds (Lewis bases) such as, for example, water (e.g. surface moisture) when applied as a thin film between the parts to be joined.
Due to the extreme reactivity of these adhesives usually inhibition of premature polymerisation which has an adverse effect on storage stability is required. Accordingly in the past acidic gases as sulphur dioxide, nitrogen monoxide, carbon dioxide, hydrogen fluoride etc. have been added to these adhesives. Furthermore proton acids including mineral acids like hydrochloric acid, sulphuric acid and polyphosphoric acid, anhydrides like phosphoric anhydride, sulfonic acids and carboxylic acids like acetic acid, itaconic acid and benzenesulfonic acid have been used as stabilizers. Typical patents relating to the aforementioned stabilizers are U.S. Pat. Nos. 2,765,332, 2,794,788, 2,756,251, 2,912,454, 2,926,188, 3,728,375, 3,993,678 and DE-OS No. 23 07 834.
However, gaseous stabilizers are only suited to a limited degree for effective stabilization of .alpha.-cyanoacrylates since metering in the liquid adhesive is difficult and during storage undefined amounts can prematurely escape. When using higher concentrations of acidic gases or non-gaseous acids the curing rate of the .alpha.-cyanoacrylates rapidly decreases. On the other hand when using too low concentrations no sufficient stabilization is achieved.
It has now been surprisingly found that the above difficulties and disadvantages of the prior art stabilizers can be obviated by the use of certain compounds described herein below as stabilizers contained in .alpha.-cyanoacrylate-based adhesive compositions. These compounds can be easily added in well defined amounts in form of solid or liquid substances, require only limited concentrations in the resulting adhesive compositions based on .alpha.-cyanoacrylate and lead to improved storage stability. Furthermore the efficiency of conventional stabilizers is greatly enhanced when combined with these compounds.